Escherichia coli RNA Polymerase Features Explained

The question asks us to identify the statement that is NOT a correct feature of Escherichia coli RNA polymerase. Let's examine each statement provided in the options based on our knowledge of bacterial transcription and E. coli RNA polymerase.

Analyzing RNA Polymerase Statements

Escherichia coli RNA polymerase is the enzyme responsible for synthesizing RNA from a DNA template. It exists in two main forms: the core enzyme and the holoenzyme.

• The core enzyme is composed of subunits $\alpha_{2}\beta\beta\rsquo;\omega$. This core enzyme is capable of binding to DNA but does so non-specifically.
• The holoenzyme is formed when the core enzyme binds to the $\sigma$ (sigma) subunit. The $\sigma$ subunit is crucial for recognizing and binding specifically to promoter sequences on the DNA, initiating transcription at the correct start site.

Now let's evaluate each statement:

1. Statement 1: "Presence of the $\sigma$ subunit along with $\alpha_{2}\beta\beta\rsquo;\omega$ core RNA polymerase is required for its promoter‐specific binding."

   This statement describes the function of the holoenzyme. The $\sigma$ subunit directs the core enzyme to specific promoter sites. Therefore, the presence of the $\sigma$ subunit makes the binding promoter-specific. This statement is correct.

2. Statement 2: "Presence of the $\sigma$ subunit along with $\alpha_{2}\beta\beta’\omega$ core RNA polymerase is not necessary for the core RNA polymerase ($\alpha_{2}\beta\beta’\omega$) to bind to the DNA template."

   This statement talks about the core enzyme's ability to bind DNA without the $\sigma$ subunit. As mentioned, the core enzyme itself can bind DNA, although this binding is non-specific. The $\sigma$ subunit is necessary for specific promoter binding, but not for DNA binding in general. Therefore, this statement is correct.

3. Statement 3: "Mutations in $\beta$ subunit in its rifampicin resistance defining region (RRDR) confer rifampicin resistance phenotype."

   Rifampicin is a well-known antibiotic that inhibits bacterial transcription by binding to the RNA polymerase $\beta$ subunit. Resistance to rifampicin often arises from mutations in the gene encoding the $\beta$ subunit, specifically within a region called the Rifampicin Resistance Determining Region (RRDR). Therefore, this statement is correct.

4. Statement 4: "Mutations in $\sigma$ subunit in its rifampicin resistance defining region (RRDR) confer rifampicin resistance phenotype."

   As discussed regarding Statement 3, rifampicin primarily interacts with the $\beta$ subunit of RNA polymerase. Mutations conferring rifampicin resistance are typically located in the $\beta$ subunit gene (rpoB), not the $\sigma$ subunit gene (rpoD for the primary housekeeping sigma). Therefore, mutations in the $\sigma$ subunit do not generally confer rifampicin resistance. This statement is incorrect.

Based on the analysis, Statement 4 is the one that is NOT a correct feature of Escherichia coli RNA polymerase.

Conclusion

The statement that is NOT a correct feature of Escherichia coli RNA polymerase is that mutations in the $\sigma$ subunit confer rifampicin resistance. Rifampicin resistance is associated with mutations in the $\beta$ subunit.